Polyethercarbonate (PEC) polyols are known in the art. PEC polyols are utilized, in conjunction with a cross-linking agent, such as an isocyanate, to produce polyurethane polymers. The polyurethane polymers can be foamed or non-foamed, i.e., elastomeric. Generally, PEC polyols are the polymerization reaction product of a H-functional initiator, an alkylene oxide, and carbon dioxide and these reactants are reacted in a reactor in the presence of a catalyst. Most recently, there has been a significant focus on using catalysts that include a multimetal cyanide compound to catalyze the reaction of the H-functional initiator, the alkylene oxide, and carbon dioxide to form the PEC polyols.
Various methods of forming PEC polyols are also known in the art. Generally, in the various methods, first and second reaction phases are present in the reactor. The first reaction phase is liquid and includes the H-functional initiator, dissolved alkylene oxide and carbon dioxide, the multimetal cyanide compound, and the forming PEC polyol. The second reaction phase is either gaseous or supercritical and includes gaseous alkylene oxide and carbon dioxide or supercritical alkylene oxide and carbon dioxide, respectively.
It has been found, however, that the solubility of CO2 in the liquid first reaction phase is very limited. The data in the following table exhibits an overall low level of CO2 solubility and also exhibits diminishing CO2 solubility with increasing temperatures in the reactor. The following table more specifically exhibits CO2 solubility, indicated as a percentage (%), in a typical polyether polyol. The typical polyether polyol has a hydroxyl number of 35 and was formed from a glycerine initiator and propylene oxide (PO) and ethylene oxide (EO) at 18% capping.
%%%%Atm0° C.Atm16° C.Atm25° C.Atm49° C.1.600.31681.670.3011.580.32101.670.30143.991.38584.171.3474.181.34454.611.25646.653.18987.073.0917.882.899910.272.34539.575.390910.325.19812.184.726516.183.746812.507.447613.487.05716.445.908721.573.998715.8410.406417.229.52321.316.997726.054.2002It has also been found that the solubility of the various components of the liquid first reaction phase in CO2 is similarly limited. That is, the solubility of the H-functional initiator, the alkylene oxide, the multimetal cyanide compound, and the forming PEC polyol in CO2 is limited.
Due to the solubility limitations described above, CO2 availability in the liquid first reaction phase is low. Because copolymerization of the alkylene oxide and CO2 to form the PEC polyol takes place in the liquid first reaction phase, incorporation of the CO2 into the PEC polyol is limited. Furthermore, reaction at the interface between the liquid first reaction phase and the second reaction phase is even more restricted and does not contribute significantly to the methods of forming the PEC polyol. Thus, the conventional methods of forming the PEC polyol and the quality of the PEC polyols that are formed are insufficient. The limited availability of CO2 in the liquid first reaction phase restricts the overall efficiency of the methods of forming the PEC polyol, leading to long reaction times and low yields. The limited availability of CO2 in the liquid first reaction phase also restricts the quality of the PEC polyols that are formed because these polyols have limited CO2 incorporation.
To combat the insufficiency of the methods of forming the PEC polyol and the PEC polyols that are formed, high CO2 pressures and/or low process temperatures are required to generate PEC polyols with adequate CO2 content. It is known that high CO2 pressures and low process temperatures are undesirable due to the high cost of high pressure equipment and due to the high catalyst (multimetal cyanide compound) concentrations and/or long cycle times required when low process temperatures are employed.
In addition to the solubility, and resulting CO2 availability, limitations described above, conventional multimetal cyanide compounds are ionic, highly polar, and therefore CO2-phobic. That is, the conventional multimetal cyanide compounds repel CO2 which is non-polar. Ultimately, this repulsion also has the effect of reducing CO2 availability in the liquid first reaction phase, specifically at catalytic sites on a surface of the multimetal cyanide compound. The conventional multimetal cyanide compounds may be further deficient by contributing to the formation of cyclic alkylene carbonates, which are undesirable byproducts. Formation of the cyclic alkylene carbonates reduces the overall yield of the desired PEC polyol.
In view of the limitations that exist in the prior art, including those described above, there remains an opportunity to improve solubility thereby increasing CO2 availability when forming the PEC polyol. There also remains an opportunity to render the catalyst, including the multimetal cyanide compound, more compatible with CO2.